Airborne Weather Radar

It's been said that thunderstorms are among the most deadly hazards faced by pilots.  It's one thing to 'see and avoid' them when you're in VMC.  But what if you're flying in cloud and/or at night?

CAR 704.64 Airborne Thunderstorm Detection and Weather Radar Equipment (Commuter)
Needed if you have passengers in IMC when thunderstorms are expected along route.


CAR 705.70 Weather Radar Equipment (Airline)
Needed if you have passengers in IMC when thunderstorms are expected along route.

Recall: RADAR = RAdio Detection and Ranging (i.e. what's out there, which direction, and how far away?).  Azimuth scan for horizontal; tilt control for vertical.

Things to remember:

• rain provides the greatest radar echo intensity
• drop size determines radar echo intensity to a much greater extent than drop number
• "hooks" and "fingers" identify areas of hail and turbulence
• when thunderstorms contour on radar displays, they should be avoided by at least 20 NM
• when flying in moderate rain, the most important key to a more informative radar display is the use of the tilt control
• tilt the antenna beam to scan the middle/lower area of a CB
• attenuation is a loss of effectiveness due to the presence of large amounts of precipitation between the radar antenna and target storm cells

Notes about lightning detection system:

• displays electrical activity associated with a storm or line of storms
• does not detect the presence or intensity of precipitation
• able to detect electrical activity from cells that are located behind mountainous terrain

The probability of lightning strikes occurring to aircraft flying within a thunderstorm area is greatest when operating at altitudes where temperatures are between -5 and +5 C.

Thunderstorms Part I

No chit-chat this time, let's get started.

Reference ACWM Chapter 15

Requirements for development of a thunderstorm:

• high relative humidity
• steep lapse rate
• lifting force / triggering action

Life cycle of a thunderstorm (1 - 3 hours):

• cumulus stage: only updrafts are present in the cloud
• mature stage: starts at onset of precipitation at the surface; updrafts and downdrafts
• dissipating stage: presence of downdrafts throughout nearly the whole cell

Classification of thunderstorms:

• airmass: form within a warm, moist air mass; isolated
• frontal: warm front (embedded in stratiform layer; least severe), cold front (form in continuous line; quite severe), trowal (rapid lifting of warm, moist air; moderate severity)
• squall line: most severe, may include heavy hail, destructive winds, tornados; often form 100-200 miles ahead of fast-moving cold fronts
• convective: formed by heating from below or by convergence of wind flow
• orographic: wind forces moist, unstable air up mountain slopes
• nocturnal: unusually warm air aloft, frequently occurs at night or early morning in Midwest / Central Plains

POP QUIZ!

You've inadvertently just flown into a thunderstorm cell.  What do you do?

Discussion of tornados, hurricanes and hazards to follow.